Here’s a bit of a unique & weird suggestion. In the game you should now be able to save claims that other countries of other land like for example, Germany has a claim on Austria and Danzig in a historical world war 2 map, I can then save that claim and then go on custom mode and open a modern day world in which I can then use that saved claims which would give Germany claims on Danzig & Austria.
This would make, making maps a lot easier, since you can now directly copy over modern day borders to your maps by making claims.
It will work similar to how you save custom settings, map styles & country colors.
This is will be basically similar to adding actual image overlays but not quite.